In modern semiconductor device applications, numerous devices are packed onto a single small area of a semiconductor substrate to create an integrated circuit. For the circuit to function, many of these individual devices may need to be electrically isolated from one another. Accordingly, electrical isolation is an important and integral part of semiconductor device design for preventing the unwanted electrical coupling between adjacent components and devices.
As the size of integrated circuits is reduced, the devices that make up the circuits must be positioned closer together in order to comply with the limited space available on a typical semiconductor substrate. As the industry strives towards a greater density of active components per unit area of semiconductor substrate, effective isolation between circuits becomes all the more important.
Isolating circuit components in modern integrated circuit technology may take the form of trench isolation structures etched into a semiconductor substrate. Once the trench isolation structures are etched in the semiconductor substrate, a dielectric material may be deposited to fill the trenches. As the density of components on the semiconductor substrate increased, the widths of the trenches sometimes decreased until the process of flowing dielectric material into the trenches developed problems.
Constrictions may develop due to a narrow opening at the top of the trench, which may be exacerbated by depth of the trench, as the dielectric material flows to an edge between a substrate surface and a sidewall of the trench. As the dielectric material flows into the trench, the constrictions may develop into voids moving into the trench with the dielectric material, which may, for instance, become filled or contaminated with conductive materials that lower the dielectric characteristics of the dielectric material used and/or introduce structural instabilities in subsequent processes.
A way to isolate high-voltage (HV) regions in, for instance, periphery devices (e.g., NAND Flash devices) is to increase the depth of trenches around the periphery of one or more arrays of memory cells. However, attempts to reduce introduction of voids into the dielectric material filling a trench isolation structure, in combination with shrinking size and spacing of the arrays, may limit the effective depth achievable in, for instance, the peripheral isolation trench structure. Limitations on the effective depth of the isolation trench structure may, in some instances, limit a voltage differential that can be isolated in a HV region without coupling and/or drainage to an adjacent region.